In the past there has been considerable study of the use of ultra sound in non-destructive and inspection of metal. Ultrasonic metal inspection is described in McGraw-Hill Encyclopedia of Science and Technology (1971) in volume 8 at page 340. Specific applications of ultra sound to metal inspection are described in U.S. Pats. No. 3,844,164, and 3,850,028.
Ultrasonic inspection apparatus heretofore available has not been well adapted for use in inspection of existing, in use, metal walls which have an extended vertical dimension such as oil refinery tanks, reaction vessels, distillation columns, steel ship hulls, and the like. Oil tanks, for example, are commonly inspected by attaching an ultrasonic transducer mounted on a carriage to a line. An operator positions himself on top of a tank and using a winch pulls in the line, thus raising the ultrasonic transducer from ground level to the top of the tank, hopefully keeping reasonably good contact between the transducer and the tank wall surface as it rises. The ultrasonic transducer is then lowered to the ground, moved laterally and again raised to the top of the tank by the line and this procedure is repeated working around the circumference of the tank.
The present invention provides apparatus capable of making rapid and efficient inspection of vertical ferromagnetic metal walls. The apparatus is placed on the vertical metal surface where it is held to the surface by four rollers formed of permanent magnetic material. The four rollers are arranged in two pairs and each pair is separately driven by a motor. Each pair of rollers may be caused to rotate at a selected rate. The rates for the two pairs may be different with the result that the apparatus can be caused to move in any desired direction, in a curved or straight path and the movement of the apparatus can be directed from ground level adjacent to the metal surface being inspected.